Collagen, the predominant matrix skin protein, is known to impart tensile strength to skin. It has been shown that collagen is significantly reduced with age and UV exposure. The degradation or destruction of the architecture of these proteins decreases the tensile strength of the skin causing wrinkles and laxity. Many studies involving human subjects have shown that collagen type I is decreased with increasing severity of photodamage (See Kligman, A., JAMA, (1969), 210, pp. 2377-2380; Lavker, R., J. Inv. Derm., (1979), 73, 79-66; Smith, J. et al., J. Inv. Derm., (1962), 39, pp. 347-350; and Shuster, S. et al., Br. J. Dermatol., (1975), 93, pp. 639-643); and some correlation in the histology of wrinkles and reduction in collagen levels in the sun-exposed skin has been reported. See Chen, S.; Kiss, I., J. Inv. Derm., (1992), 98. pp. 248-254. Voorhees and collegues have supported these findings by showing the restoration of collagen type I in photo-damaged human skin by a topical treatment with tretinoin. See Christopher, E., et al., The New Eng. Jou. of Medicine (1993), 329, pp. 530-535. These results provide the first in vivo evidence that retinoic acid restores collagen type I. Many etiology studies showed a parallel effect between collagen synthesis and wrinkle effacement. It is also believed that the strengthening of the dermal matrix by collagen stimulation may have some beneficial effect for treatment of cellulite. See U.S. Pat. No. 5,051,449 (Kligman).
There are a few natural products which are known to stimulate collagen synthesis. One of these is ascorbic acid, a cofactor for collagen synthesis, known to activate the enzyme prolyl-hydroxylase (See Peterkofsky, B., Arch. Biochem. Biophys., (1972), 152, pp. 318-328) and to increase procollagen mRNA. See Cardinale, G. et al. Adv. Enzymol., (1974), 41, p. 245; Geesin, J. et al., J. Inv. Derm., (1988), 90, p. 420; Tajima, S. et al., Biochem. Biophys. Res. Comm., (1982), 106, pp. 632-637. Stimulation of collagen synthesis by betel nut alkaloids, arecolin and arecaidine, has also been described. See Vermillo, A. et al. Arch. Oral Biol., (1986), 31, pp. 819-823. Forskolin which is a common component of Coleus forskolli has been shown to increase the production of collagen in cloned osteoblastic cells. See Hakeda, Y. et al., J. Biochem., (1987), 101, pp. 1463-1469. Excluding ascorbic acid, these agents are not acceptable for cosmetic or personal care use due to their potential toxicity.
Some studies indicate that Centella asiatica promotes greater elasticity and suppleness to the skin by its action on the collagen synthesis by the fibroblasts. See Tenni, R. et al., J. Biochem, (1988), 38. pp. 69-77; Maquart, F. et al., Actualite Therapeutique, (1989), pp. 1571-1574. Centella asiatica also acts as a regulating agent in the connective tissue, promoting its regeneration and preventing its excessive proliferation, producing supple, healthy connective tissue. See Lawrence J. Eur. J. Pharmacol., (1967), pp. 414-425; Rosen, H. et al., J. Proc. Soc. Exp. Biol. Med., (1967), 125, pp. 279-280; Bosse, J. et al.; Ann. Plast. Surg., (1979), 3, pp. 13-21. Vogel et al. have shown a significant increase of collagen in scar tissue leading to an increased resistance to traction and rupture. See Vogel, H. et al., Acta Therapeutica, (1990) 16, pp. 285-296. This increased resistance of the collagen fibers is only noticeable in collagen which has reached a certain maturation stage. The triterpenes of Centella asiatica increase both the collagen synthesis and its maturation level.
The plant, Centella asiatica, grows in Madagascar and around the Indian Ocean. Traditionally, this plant has been used for wound healing. See Chopra, R. et al., "Indigenous Drugs of India", Dhur & Sons Pvt. Ltd. (1985), Calcutta. In Europe, a drug prepared from this plant is used for the treatment of ulcers and wounds. Centella asiatica is also suitable for cosmetic use, i.e., skin conditioning improvement, anti-cellulite effect, and improvements in skin color. See Adolphe, M. et al., Int. J. Cosmetic Soc., (1984), 6, pp. 55-58. Centella asiatica contains asiatic acid, madecassic acid, asiaticoside and madecaside, all of which belong to the class of triterpenoids. Maquart et al., Conn. Tissue Res., (1990), 24 pp. 107-120 showed that the triterpene extract from Centella asiatica stimulated collagen synthesis in fibroblast monolayer cultures, and asiatic acid was found to be the major component responsible for collagen synthesis stimulation.
The present invention is based at least in part on the discovery that betulinic acid has better collagen stimulation activity than Centella asiatica extract or active components of Centella asiatica. Unlike the structural configuration of triterpenes like asiatic acid or asiaticoside, betulinic acid has a fused five member ring and contains exo-vinyl group as illustrated in Figure below. The use of betulinic acid and plants containing betulinic acid in foods and flavors has been disclosed. See JP 051776688A; JP 57031620A.
It is an object of the present invention to provide cosmetic compositions containing an active component which is safe, yet is more effective than Centella asiatica or the active components of Centella asiatica.
It is another object of the present invention to provide cosmetic compositions containing betulinic acid.
It is yet another object of the invention to provide a method of treating skin and of stimulating collagen synthesis in skin.
These and other objects of the invention will become more apparent from the detailed description and examples that follow.